The invention relates generally to water heaters and in particular to dual energy gas and electric water heaters and to safety circuits therefor. Traditionally, water heaters have been energized by a variety of sources, including electricity and combustion of natural gas, both drawn from local distribution networks. In most populated areas today, residences and other types of facilities including businesses, industrial plants, retail facilities, educational facilities, and government facilities, generally have access to local distribution networks of both electricity and natural gas, and thus the decision on whether to operate water heaters, furnaces, and similar energy intensive equipment is based on current economic conditions affecting the price and immediate availability of electricity and natural gas.
Energy price swings and supply interruptions can occur with little warning, and facilities operators have long sought to maintain dual energy systems that can be switched as necessary, for example, with water heaters that may be energized by either electricity or natural gas. The prior art teaches a number of dual energy water heater systems whose specialized adaptations are focused on rapid, automated, and unattended switching between energy supplies over timescales of seconds up to hours. However, such systems and their attendant management complexity are unnecessary where many homeowners and facility operators want to respond to energy price shifts and supply issues over longer timescales of days up to weeks, and have a more deliberate, manual, and cheaper transition. Such timescales are generally too short and frequent for the regular replacement of a single energy source water heater with another of the other type, but long enough where automated control systems are not necessary.
Dual energy systems in the field of water heaters will necessarily face the problem of disabling the not-in-use energy source when the other is in use, specifically disabling the ability of the system to burn gas while the electric heating system is active and vice versa. The prior art systems have generally addressed this by disabling the gas supply by providing automatic gas flow control. However, the gas igniter generally remains in electrical communication with the ignition point of the gas burner. This creates a potential safety hazard of an unnecessary spark from the unexpected activation of the igniter, even if the gas supply is disabled, whether electronically or manually.
The present invention aims to address these shortcomings of the prior art by providing a dual-energy gas and electric water heater equipped with a safety circuit that disables the gas igniter whenever the electrical heating system is connected to wall power, and where an electrical quick connect is provided for the purpose of easily powering and depowering the electrical heating system. The igniter is intended to be enabled whenever the electrical system is without power, either from being disconnected or from a power outage. The invention may be used in conjunction with manual enablement and disablement of the natural gas supply, or in combination with prior art systems that automatically disable and enable the gas supply.